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Dependency Modelling for Cultural Heritage
Joel Taylor, Nigel Blades
and May Cassar
CENTRE FOR SUSTAINABLE HERITAGE
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Undesirable Events:Gare de Montparnasse, Paris, 1895
Late train travelled fast to make up time, so air brakes were required to stop before the terminal.
The locomotive brakes were insufficient and the air brakes failed.
The conductor was pre-occupied with paperwork and didn’t apply the handbrake.
Terminal barrier and 30m of station were insufficient to stop the train.
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Risk Chain
release
exposure
attack consequence
Risk assessment
Dosimetry Condition assessment
Environmental monitoring
Part of this is determining which points are critical for hazards to have an effect on a collection
There are various ways of assessing and mitigating damage which relate to different stages of the process
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Dependencies in Risk
Outcomes are dependent on a series of prior events, which can be generalised.
What needs to take place for damage to happen?
What are the critical points and pathways in this chain of events?
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These are deductive, top-down methods of analysing risks in system design.
It involves specifying a ‘top event’ to analyse (damage).
Then identifying all of the elements in the system that could cause the ‘top event’ to occur.
Dependency Modelling
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Its Application
Concept was developed by Bell Telephones in 1962, as a way of detecting weak points in systems, then adopted and then improved by Boeing.
Although originally used to assess system reliability, it is now applied to many things.
Requires an understanding of the relationships in the system (boundary conditions).
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Damage to object from
pollution
Exposed surfaces for deposition
Interaction of pollutant with
collection
Presence of pollutant in
building
No attractive deposition surfaces
Generation of pollutant internally
Infiltration through natural
ventilation
AND
AND
OR
Infiltration through HVAC
An example
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Relationships in the Model
In a positively phrased dependency model, AND dependencies are points of weakness because all events need to occur for the higher event to take place.
OR dependencies represent points of strength, because of alternatives options. Can turn these into ANDs through investigation.
Probabilities can be applied to each event, so cost effectiveness and efficiency can be determined for any action.
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Modelling Deterministic Risk
Events often about extent of impact, not presence or absence of impact.
Deterministic risks do not rely on specific events, so cannot be modelled this way.
The threshold levels can be used to create ‘steps’ for each event, so pathway has defined levels, e.g. presence is NO2 at 10 ppb, rather than 5ppb.
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Deposition rate affected by Temp
and RH
Damage to objects from 5ppb NO2 over one year
Presence of pollutant in cases
Presence of NO2 in gallery
Objects in case
Infiltration from outside
Internal generation
Intake filtration
Poor seals in cases
External presence
of NO2
Intake position
HVAC filter
Cellulose nitrate
breakdown
Unflued heating
appliance
Reaction from NO2
No attractive deposition surfaces
Presence of NO2 in building
AND
AND
AND OR
OR
OR
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Deposition rate affected by Temp
and RH
Damage to objects from 5ppb NO2 over one year
Presence of pollutant in cases
Presence of NO2 in gallery
Objects in case
Infiltration from outside
Poor seals in cases
External presence
of NO2
Intake position
No attractive deposition surfaces
Presence of NO2 in building
AND
AND
AND
Building displaying
objects
AND
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Cultural Heritage Applications
The most cost effective approach to
mitigating a hazard can be determined.
Can be reversed to assess reliability of
proposed mitigation method.
Can be applied to
moveable and
immoveable heritage.
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Developing the Models
Events can be classified ‘top’, ‘intermediate’, ‘undeveloped’ and ‘initiating’.
Can develop templates for different risks.
Can apply the synergistic effect of risks to dependency model.
Can vary top events, and therefore relate to tangible or intangible issues.
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Thank You
MASTER Project Partners
Peter McLennan, UCL
Barry Holt, National Safety Council (Europe)
European Commission
You